Just adding my +1 for the 10/01/07 patch on
<http://dev.rubyonrails.org/ticket/6868> - add_column in the postgres
adapter ignoring precision and scale.
The patch is tiny and looks solid to me. The included test runs fine
with postgres and sqlite3.
Line numbers are off compared to current trunk. I'm not sure if that
matters for a one-liner + self contained test method, but could update
the patch if desired.